Radio frequency (RF) filters are used in wireless communication systems. Two types of RF filters are Surface Acoustic Wave (SAW) filters and Bulk Acoustic Wave (BAW) filters. A SAW filter typically comprises a pair of interdigitated electrical conductive traces formed on a surface of a piezoelectric material. A BAW filter typically comprises a piezoelectric material sandwiched between two electrodes and acoustically isolated from the surrounding medium. SAW filters are generally used at relatively lower frequencies, e.g., below 2.5 GHz, whereas BAW filters are generally used at relatively higher frequencies, e.g., above 2.5 GHz. SAW and BAW devices may be formed and subsequently attached to a substrate or circuit board using, e.g., flip chip techniques.
Alternatively, SAW and BAW devices may be incorporated into an integrated circuit (IC) chip at the wafer level, e.g., during CMOS (complementary metal oxide semiconductor) processing. The latter approach, i.e., forming RF filters at the wafer level during CMOS processing, eliminates the need for additional chips. However, integrating RF filters, including SAW and BAW filters, at the wafer level during CMOS processing is difficult due at least in part to the fabrication scale on monolithic devices.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.